The present invention relates to a method and apparatus for repairing pixel defects in liquid crystal display devices.
Among the defects which occur in the manufacturing process of liquid crystal display devices, there are defects so serious that the subject liquid crystal display device must be scrapped. When the defects are not so serious, the device may be considered a good product and shipped even if that defect is left as is.
For example, in the case of normally white display devices of which pixels are white while voltage is not applied, defective pixels that allow light pass through themselves when voltage is applied and non-defective pixels are driven black (hereinafter referred to as “light point defect” pixels) are quite easy to recognize considering human visual perception characteristics and thus become conspicuous defects. Consequently, liquid crystal display devices having light point defects are usually treated as defective products and cannot be shipped as good products.
Light point defects occur due to a variety of causes, such as opened contact hole, residual ITO fragments, inter-electrode leaks in the thin film transistors and the like which make up the pixel circuits, inter-pixel shorts due to foreign matter such as metal fragments, and light scattering due to foreign matter. As a result, it is difficult to repair each defect by a method corresponding to each cause.
On the other hand, defective pixels which remain black when voltage is applied and non-defective pixels are driven white (hereinafter referred to as “black spot defect” pixels) are less striking to human eyes than pixels with light point defects. As a result, even if a liquid crystal display device has black spot defects, depending on their extent, in some cases the products may be treated as good.
In this regard, methods have been studied which aim, by applying some kind of processing to light point defects and converting them to black spot defects and thus repairing defective products, to increase yields and reduce production cost. For example, in Patent Laid-Open Publication No. Hei 9-90304 a method is proposed whereby conversion to black spot is accomplished by irradiating a defective pixel of a liquid crystal device with a first laser light, thus causing air bubbles to form in the liquid crystal layer peripheral to and including the defective pixel, and in this state where air bubbles have been formed, irradiating that defective pixel with a second laser light so that, through that energy, the constituent material of that defective pixel is made to spatter within the air bubble causing the adhesion and accumulation of the spattered matter onto the opposing electrodes of the liquid crystal display device.